1. Field of the Invention:
This invention relates to an improvement on a drive source for a slit exposure shutter in which shutter blades are arranged to be caused to travel by an electromagnetic drive.
2. Description of the Prior Art:
Advancement of application of electronics to cameras has during recent years prompted proposals of various electromagnetically driven shutters using electromagnetic driving devices adapted for use as drive sources for slit exposure shutters. Compared with the conventional mechanically driven shutter, the shutter of this type has a drive mechanism simply arranged to permit reduction in size, weight and cost of a camera and is thus highly suitable for a camera that has electronics applied thereto to an advanced extent. However, a space available within a camera for housing a power source is limited and allows the use of only a small battery of small electrical capacity. Accordingly, the electric current available from such a power source is also limited calling for a minimal power consumption and thus it is not desirable to take out a large current therefrom. An electromagnetic drive source for driving a shutter, therefore, has been required to be capable of efficiently driving shutter blades at a high speed with a small power. Further, in order to permit reduction in weight of a shutter, it has been desired to have a slit exposure type shutter arranged to drive light weight shutter blades directly with a rotary electromagnetic drive source.
In a slit exposure shutter of the type arranged to have the front and rear shutter blades driven respectively by a rotary electromagnetic drive source to perform exposure effecting and returning travels, the rotor of the electromagnetic drive source makes a reciprocative rotational movement within a preset range of rotation angle. The rotation angle does not exceed 180.degree.. The shutter blades are caused to make an exposure effecting travel by the onward rotational movement while the return travel of the shutter blades is caused by the backward rotational movement. It is, however, possible to have the shutter blades caused to make an exposure effecting travel also by the backward rotational movement. In the device of such a type, the rotor of the drive source is under the load of the shutter blades imposed always in one direction during the reciprocative rotational movement. Such a condition necessitates a flow of a large driving current to the drive source in order to drive such a load.